Throughout this application one or more publications are referenced with parentheses. The disclosures of such publications in their entireties are hereby incorporated by reference in this application in order to more fully describe the state of the art to which this invention pertains.
1. Field of the Invention
The present invention relates generally to optical switching. In particular, the invention relates to methods, devices and systems to optically switch a specific channel of light between optical fibers.
2. Discussion of the Related Arts
Dielectric microspheres are known in the art. It has been shown that a microsphere of the appropriate proportions can form a wavelength specific connection from one optical fiber to another by virtue of the dielectric microsphere""s resonance in a whispering gallery mode (WGM) for the specific wavelength. The WGM may be used to switch light transmission from one optical fiber to another. Depending on the placement of the microsphere and nature of the optical fibers, fairly high efficiency of light transfer may be achieved. Ming, Cai and Kerry Vahala Opt. Lett 25, No. 4, 260 (2000).
Wavelength Division Multiplexing (WDM) is a technique which has been used to enhance the signal capacity of a single mode optical fiber by simultaneously transmitting multiple discreet wavelengths of light, referred to as xe2x80x9cchannelsxe2x80x9d in a single band. The wavelengths in each channel are separated by a pre-determined spacing usually in the order of hundreds of GHZ. Dense Wavelength Division Multiplexing (DWDM) systems are characterized by closer spacing between the respective wavelengths comprising the channels thereby allowing for a greater number of channels within the same band in the same optical fiber as compared to WDM.
The speed of routing from one optical fiber to another is limited by the rate at which the optical switching occurs. In the past, switches which convert the optical data to electronic data have been a xe2x80x9cbottleneckxe2x80x9d in the system. Those acquainted with optical switching will recall that much interest has been shown in achieving the goal of a direct optical to optical switch which would eliminate the bottleneck caused by the optical to electronic conversions of the past. A variety of devices have been developed in pursuit of achieving this goal.
Common to many optical to optical switches and optical routers is an all or nothing functionality by which the entire signal, within a channel, is switched or not switched. While useful for small or local networks, especially those networks with easily controlled light sources (lasers), in larger or less controlled environments an optical router must be able to accept signals from a variety of sources and seamlessly multiplex despite, difference in the quality of the signals. Optical switches lacking the ability to monitor, equalize and/or groom the channels in nanoseconds or even picoseconds, (which is xe2x80x9creal timexe2x80x9d for optical transmissions) may yield turbidity within a band resulting in unbalanced light transmissions (signals) from channel to channel which in turn may cause noise, loss of part of a signal or channels to drop out.
Accordingly, there exists a need for an optical switch and router that operate in xe2x80x9creal timexe2x80x9d (which is in the order of nanoseconds or picoseconds) for light transmission. There also exists a need for an optical router of xe2x80x9creal timexe2x80x9d optical switches which can monitor, groom, and/or balance a channel relative to the other channels in an optical band. The present invention satisfies these needs and others and provides related advantages.
The present invention provides a novel and improved method, system and device to rapidly (in the range of nanoseconds and event picoseconds) route signals from particular channels within an optical band by using optical switches which utilize the whispering gallery mode (WGM) resonance of dielectric microspheres to optically switch signal. All references made hereinafter to microsphere(s) shall refer to dielectric microsphere(s).
In all embodiments an optical router is formed of a series of optical switches. Common to the optical switches is the placement of a microsphere in proximity to the unclad or thinly clad regions of a pair of optical fibers. To switch the signal of a particular channel (wavelength of light) between optical fibers, the evanescent waves emanating from the electromagnetic fields associated with the signal in the particular channel are allowed to resonate across a wavelength specific microsphere via the WGM of the microsphere to another optical fiber.
In one embodiment of the optical router, the optical switches are formed of microspheres. Each microsphere has a steady state index of refraction xe2x80x9cnxe2x80x9d and will resonate in WGM for a specific wavelength of light (channel) when positioned between optical fibers at a region of thinned or removed cladding with substantially similar indexes of refraction.
Switching is accomplished by controlling the steady state index of refraction xe2x80x9cnxe2x80x9d of a microsphere. A pair of electrodes placed on either side of each microsphere can be used to apply a voltage across the microsphere. When an adequate voltage is applied across the electrode pair the steady state index of refraction xe2x80x9cnxe2x80x9d of the microsphere is altered by the polarizing effect of the voltage on the substrate of the microsphere. The polarization changes the dielectric constant of the substrate which in turn alters the steady state index of refraction xe2x80x9cnxe2x80x9d of the microsphere. In the case where the steady state index of refraction xe2x80x9cnxe2x80x9d of the microsphere is substantially similar to the index of refraction of the optical fibers the voltage will cause the steady state index of refraction xe2x80x9cnxe2x80x9d of the microsphere to become sufficiently dissimilar from the index of refraction of the optical fibers to preclude WGM resonance.
To switch a particular optical switch within the optical router the voltage across the electrode pair need only be briefly interrupted (in the order of a few nanoseconds to a few picoseconds), to allow the signal to pass from one optical fiber to another. Accordingly, an optical router useful for WDM, DWDM and wavelength division de-multiplexing is achieved.
Conversely, by selecting a microsphere with a steady state index of refraction xe2x80x9cnxe2x80x9d dissimilar to the index of refraction of the optical fibers and applying sufficient voltage across the electrode pair to alter the index of refraction of the microsphere it would be substantially similar to the index of refraction of the optical fibers thereby enabling WGM resonance of the microsphere while the voltage is applied.
Adjustment of the voltage may also provide for a controllable index of refraction of xe2x80x9cnxc2x1x,xe2x80x9d for the microsphere, wherein as xe2x80x9cxxe2x80x9d approaches zero the efficiency of the transfer of signal approaches the microsphere""s maximum obtainable efficiency which may be useful for applications such as channel equalizing, grooming and power balancing.
In another embodiment, a plurality microspheres are provided, each with a light activated material, such as a dye, integrated within their substrate. To form the optical router, a series of optical switches, each containing microspheres selected to resonate in WGM for specific channels, are positioned in close proximity to an unclad or thinly clad region in each of two optical fibers.
Each optical switch operates by controlling the irradiation of the microsphere with an appropriately intense beam of light. The irradiation will activate the light activated material and depending on the selection of the light activated material and microsphere substrate, the irradiation will either change the dielectric constant of the light activated material and affect the average dielectric constant of the microsphere, or affect the dielectric constant of the light activated material and the substrate, thereby altering the dielectric constant of the microsphere. In either case, the change in the dielectric constant will alter the steady state index of refraction xe2x80x9cnxe2x80x9d of the microsphere.
If the steady state index of refraction xe2x80x9cnxe2x80x9d of the microsphere is substantially similar to the index of refraction of the optical fibers, the irradiation can be used to alter the steady state index of refraction xe2x80x9cnxe2x80x9d to become dissimilar to that of the optical fibers and disrupt the WGM resonance. A practical application of such a microsphere would be to maintain an appropriately intense beam of light directed at the microsphere until switching of the channel corresponding to that microsphere is required. A brief interruption in the intense beam of light will result in switching. On the other hand, if the steady state index of refraction xe2x80x9cnxe2x80x9d of the microsphere is dissimilar to the index of refraction of the optical fibers, a brief pulse of irradiation can be used to alter the index of refraction xe2x80x9cnxe2x80x9d of the microsphere to become substantially similar to the index of refraction of the optical fibers and thereby switch the channel by enabling the WGM resonance.
In either case, by passing the intense beam of light through a Mach-Zender interferometer the speed at which the intense beam of light can be pulsed xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d is in the range of nanoseconds to picoseconds.
Moreover, adjustment of the intensity of the intense beam of light, in either case, may also provide for a controllable index of refraction of xe2x80x9cnxc2x1x,xe2x80x9d for the microsphere, wherein as xe2x80x9cxxe2x80x9d approaches zero, the efficiency of the transfer of signal approaches the microsphere""s maximum obtainable efficiency which may be useful for applications such as channel equalizing, grooming and power balancing.
In another embodiment of an optical router, each microsphere comprising a specific optical switch has a steady state index of refraction xe2x80x9cnxe2x80x9d which always corresponds to the index of refraction of the optical fibers. Optical switching occurs when the selected microsphere is physically contained within an optical trap an moved towards the unclad or thinly clad regions of two optical fibers. At some proximity from the optical fibers the evanescent wave, associated with the signal of the selected channel, will traverse the surface of the selected microsphere via WGM resonance, and switch signal one optical fiber to another optical fiber. When the switching is completed, the optical trap is quickly withdrawn and the microsphere ceases to resonate the signal in WGM.
Adjustment of the proximity of the microsphere to the stripped or thinly cladded region of the optical fibers will provide a controllable index of refraction of xe2x80x9cnxc2x1xxe2x80x9d for the microsphere, wherein as xe2x80x9cxxe2x80x9d approaches zero, the efficiency of the transfer of signal approaches the microsphere""s maximum obtainable efficiency which may be useful for applications such as channel equalizing, grooming and power balancing.
In each embodiment the routing of the appropriate wavelength of light from one optical fiber to another is dependent on the propagation of an evanescent wave to a corresponding microsphere which acts in a WGM. The switching xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d of the microsphere is either by physical movement or by altering the microsphere""s steady state index of refraction xe2x80x9cnxe2x80x9d.